This invention relates to a supported noble metal catalyst composition and to a process for selectively hydrogenating a highly unsaturated hydrocarbon employing a supported noble metal catalyst composition.
Catalysts comprising palladium and an inorganic support are known catalysts for the hydrogenation of polyenes and/or alkynes. Even though these catalysts are effective hydrogenation catalysts, they ten to produce green oil by oligomerizing alkenes, polyenes, and/or alkynes. Green oil, as used herein, refers to molecules having 6 or more carbon atoms per molecule and is undesirable in the production of an alkene because it fouls the hydrogenation catalyst which in turn deactivates the catalyst. The deactivation process can lower the activity and selectivity of the catalyst. Therefore, there is an ever present need for further improvements in the selective hydrogenation process for converting a highly unsaturated hydrocarbon to a less unsaturated hydrocarbon and to achieve enhanced selectivity to the less unsaturated hydrocarbon, or increased catalyst life, or both. Accordingly, the development of a modified supported palladium catalyst composition and its use in processes for the selective hydrogenation of highly unsaturated hydrocarbons such as diolefins (alkadienes) or alkynes to less unsaturated hydrocarbons such as monoolefins (alkenes) would be a significant contribution to the art.
It is an object of this invention to provide a palladium-containing catalyst composition which can be useful as a catalyst in the selective hydrogenation of a highly unsaturated hydrocarbon such as a diolefin and/or alkyne to a less unsaturated hydrocarbon such as a monoolefin. It is another object of this invention to employ this catalyst composition in the selective hydrogenation of highly unsaturated hydrocarbons such as diolefins or alkynes to monoolefins. An advantage of this invention is the increased or enhanced selectivity to a desired product and the decreased production of oligomers which form green oils, thereby increasing the life cycle of the catalyst. Other objects and advantages will become more apparent as the invention is more fully disclosed hereinbelow.
According to a first embodiment of this invention, a catalyst composition is provided which comprises, consists essentially of, or consists of palladium, an inorganic support material, and a selectivity enhancer which is silver, phosphorus, sulfur, or combinations of two or more thereof. The inorganic support can be a spinel, alumina, silica, titania, zirconia, an aluminosilicate, an aluminate such as zinc aluminate, magnesium aluminate, calcium aluminate, or combinations of two or more thereof.
According to a second embodiment this invention, a process which can be used for selectively hydrogenating a highly unsaturated hydrocarbon to a less unsaturated hydrocarbon is provided. The process comprises contacting a highly unsaturated hydrocarbon with hydrogen, in the presence of a catalyst composition, under a condition sufficient to effect a selective hydrogenation of the highly unsaturated hydrocarbon. The catalyst composition can be the same as the composition disclosed in the first embodiment of this invention.
As used in the present invention, the term xe2x80x9cfluidxe2x80x9d denotes gas, liquid, or combination thereof. The term xe2x80x9cselectivity enhancerxe2x80x9d denotes an element or compound which enhances the selectivity to an alkene, decreases the selectivity to an alkane, or decreases the selectivity to an undesirable product such as green oils when the composition of the invention is employed as a catalyst in a selective hydrogenation process disclosed in this invention. The term xe2x80x9csubstantialxe2x80x9d or xe2x80x9csubstantiallyxe2x80x9d generally means more than trivial. A xe2x80x9csaturated hydrocarbonxe2x80x9d is referred to as any hydrocarbon which does not contain any carbon to carbon multiple bonds. An xe2x80x9cunsaturated hydrocarbonxe2x80x9d as used in this invention is a hydrocarbon having at least one double bond or triple bond between carbon atoms in the molecule. Example of saturated hydrocarbons include, but are not limited to, ethane, propane, butanes, pentanes, hexanes, octanes, decanes, naphtha, and combinations of any two or more thereof. Examples of unsaturated hydrocarbons include, but are not limited to, monoolefins such as ethylene, propylene, butenes, pentenes, hexenes, octenes, and decenes; aromatic compounds such as benzene and naphthalene; alkynes such as acetylene, propyne, and butynes; diolefins such as propadiene, butadienes, pentadienes (including isoprene), hexadienes, octadienes, and decadienes; and combinations of two or more thereof. The term xe2x80x9chighly unsaturated hydrocarbonxe2x80x9d refers to a hydrocarbon which contains a triple bond or two or more double bonds in a molecule. The term xe2x80x9cless unsaturated hydrocarbonxe2x80x9d refer to a hydrocarbon in which the triple bond in the highly unsaturated hydrocarbon is hydrogenated to a double bond or a hydrocarbon in which the number of double bonds is one less, or at least one less, than that in the highly unsaturated hydrocarbon. The term xe2x80x9cselective hydrogenationxe2x80x9d is referred to as a hydrogenation process which converts a highly unsaturated hydrocarbon such as an alkyne or a diolefin to a less unsaturated hydrocarbon such as a monoolefin without hydrogenating the less unsaturated hydrocarbon to a more saturated hydrocarbon or a saturated hydrocarbon such as alkane.
The composition of this invention comprises, consists essentially of, or consists of (a) palladium such as palladium metal, palladium oxide, or combinations thereof in which the palladium can be present as a xe2x80x9cskinxe2x80x9d distributed on the surface of an inorganic support, (b) an inorganic support selected from the group consisting of alumina, silica, titania, zirconia, aluminosilicates (clays and/or zeolites), a spinel such as zinc aluminate, zinc titanate and magnesium aluminate, and combinations of two or more thereof, (c) a selectivity enhancer selected from the group consisting of silver, silver compounds, phosphorus, sulfur, phosphorus compounds, sulfur compounds, potassium, potassium compounds, and combinations of two or more thereof, and optionally (d) a fluorine- or fluoride-containing compound. Examples of suitable selectivity enhancer compounds include, but are not limited to, silver, silver nitrate, silver chloride, potassium phosphate, sodium phosphate, ammonium phosphate, sodium sulfate, potassium sulfate, ammonium sulfate, and combinations of two or more thereof. The term xe2x80x9cphosphatexe2x80x9d also includes dibasic and monobasic phosphates. Examples of suitable fluorine- or fluoride-containing compounds include, but are not limited to, non-alkali metal fluorides such as ammonium fluoride, hydrogen fluoride, and ammonium hydrogen fluoride; alkali metal fluorides such as sodium fluoride, potassium fluoride rubidium fluoride, and cesium fluoride; and combinations of two or more thereof.
Generally, the composition can contain about 0.001 to about 3, preferably about 0.001 to about 2 weight % Pd; about 0.002 to about 10, preferably about 0.01 to about 5 weight % each selectivity enhancer; optionally about 0.002 to about 10, preferably about 0.01 to about 5 weight % fluorine; and the rest being inorganic support. The composition can have any suitable shape such as spherical, cylindrical, trilobal, or combinations of two or more thereof. The preferred shape is either spherical or cylindrical. The particles of this catalyst generally have a size of about 1 to about 10 mm, preferably about 2 to about 6 mm. Generally the surface area of the catalyst as measured by the BET method (Brunauer, Emmett and Teller) employing N2 is 0.5 to about 200, preferably about 1 to about 100 m2/g.
The composition can be produced by any suitable means known to one skilled in the art. For example, the components (a) and (c) as well as the optional component (d) can be deposited onto and/or incorporated into the inorganic support by any suitable means. For instance, the selectivity enhancer(s) can be incorporated, such as by impregnation or spraying, into the support material before it is incorporated or impregnated with a suitable palladium compound, and preferably also with a suitable silver compound. Alternatively, at least one alkali metal compound can be incorporated, such as by impregnation or spraying, into the catalyst simultaneously with or after the impregnation with a suitable palladium compound. When silver is also present in the catalyst composition, then at least one selectivity enhancer can be incorporated between the palladium and silver impregnation steps or after the impregnation of the palladium and silver compounds. In the presently preferred catalyst preparation, a supported Pd/Ag catalyst material, more preferably Pd/Ag/Al2O3 which can be produced by the method described in U.S. Pat. Nos. 4,404,124 and 4,484,015, is impregnated with an aqueous solution of at least one catalyst modifier, followed by drying, generally at 50xc2x0 C. to 150xc2x0 C., and optionally calcining, preferably in air at a temperature of 300xc2x0 C. to 700xc2x0 C., more preferably at 350xc2x0 C. to 650xc2x0 C., preferably for 0.5 to 20 hours, more preferably from 1 to 10 hours.
A non-alkali metal fluoride, preferably HF, NH4F, or NH4HF2 or combinations of two or more thereof, can be incorporated into the catalyst in any suitable manner. The non-alkali metal fluoride can be incorporated together with palladium and a selectivity enhancer and preferably a suitable silver compound. Preferably, the non-alkali metal fluoride can be incorporated after the impregnation of the solid inorganic support with palladium and at least one selectivity enhancer and, preferably, also a suitable silver compound. After the incorporation of Pd, any selectivity enhancer(s), fluoride and, preferably also silver into the inorganic support been completed as described above, the resultant material can be dried, generally at about 50xc2x0 C. to 150xc2x0 C., for about 0.01 to 10 hours, and then optionally calcined, generally at a temperature of about 300xc2x0 C. to 700xc2x0 C., for about 0.5 to 20 hours. Optionally, the catalyst can be reduced with hydrogen gas, preferably at 10xc2x0 C. to 200xc2x0 C. for about 0.1 to 20 hours, so as to reduce the oxides of palladium and silver, if present, to the corresponding metal(s).
According to the second embodiment of this invention, a selective hydrogenation process is provided. The selective hydrogenation process of this invention can comprise, consist essentially of, or consist of contacting feed which contains one or more highly unsaturated hydrocarbon(s), in the presence of hydrogen, with the catalyst composition disclosed above. Preferably the feed containing the highly unsaturated hydrocarbon(s) also comprises an unsaturated hydrocarbon(s). The highly unsaturated hydrocarbon is present as an alkyne, a polyene, such as a diolefin, or combinations of two or more thereof, as an impurity, generally at a level of about 1 mg/Kg (ppm) to about 50,000 ppm each in the feed. The unsaturated hydrocarbon(s) in the feed can be one or more alkenes.
Examples of suitable alkynes include, but are not limited to, acetylene, propyne, 1-butyne, 2-butyne, 1-pentyne, 2-pentyne, 3-methyl-1-butyne, 1-hexyne, 1-heptyne, 1-octyne, 1-nonyne, 1-decyne, and combinations of two or more thereof. The presently preferred alkynes are acetylene and propyne.
These alkynes are primarily hydrogenated to the corresponding alkenes. For example, acetylene is primarily hydrogenated to ethylene, propyne is primarily hydrogenated to propylene, and the butynes are primarily hydrogenated to the corresponding butenes (1-butene, 2-butenes).
Examples of suitable polyenes include those containing about 3 to about 12 carbon atoms per molecule. The presently preferred polyenes are diolefins. Such diolefins include, but are not limited to, propadiene, 1,2-butadiene, 1,3-butadiene, isoprene, 1,2-pentadiene, 1,3-pentadiene, 1,4-pentadiene, 1,2-hexadiene, 1,3-hexadiene, 1,4-hexadiene, 1,5-hexadiene, 2-methyl-1,2-pentadiene, 2,3-dimethyl-1,3-butadiene, heptadienes, methylhexadienes, octadienes, methylheptadienes, dimethylhexadienes, ethylhexadienes, trimethylpentadienes, methyloctadienes, dimethylheptadienes, ethyloctadienes, trimethylhexadienes, nonadienes, decadienes, undecadienes, dodecadienes, cyclopentadienes, cyclohexadienes, methylcyclopentadienes, cycloheptadienes, methylcyclohexadienes dimethylcyclopentadienes, ethylcyclopentadienes, dicyclopentadiene, and mixtures of one or two of these diolefins. Presently preferred diolefins are propadiene, 1,3-butadiene, pentadienes (such as 1,3-pentadiene, 1,4-pentadiene, isoprene), cyclopentadienes (such as 1,3-cyclopentadiene) and dicyclopentadiene (also known as tricyclo[5.2. 1]2,6deca-3,8-diene). These diolefins are preferably hydrogenated to their corresponding monoolefins containing the same number of carbon atoms per molecule as the diolefins. For example, propadiene is hydrogenated to propylene, 1,3-butadiene is hydrogenated to 1-butene and 2-butene, 1,3-pentadiene and 1,4-pentadiene are hydrogenated to 1-pentene and 2-pentene, isoprene is hydrogenated to methyl-1-pentenes and methyl-2-pentenes, and 1,3-cyclopentadiene is hydrogenated to cyclopentene.
The highly unsaturated hydrocarbon-containing feed for the hydrogenation process of this invention can also comprise one or more additional hydrocarbons, in particular, monoolefins, aromatic hydrocarbons, and saturated hydrocarbons. Examples of such other hydrocarbons which can be present in the feed at a level of 0.001 to 99.999 weight % include, but are not limited to, ethylene, propylene, 1-butene, 2-butene, isobutylene, 1-pentene, 2-pentene, methyl-1-butenes (such as 2-methyl-1-butene), methyl-2-butenes (such as 2-methyl-2-butene), 1-hexene, 2-hexene, 3-hexene, methyl-1-pentenes, 2,3-dimethyl-1-butene, 1-heptene, 2-heptene, 3-heptene, methyl-1-hexenes, methyl-2-hexenes, methyl-3-hexenes, dimethylpentenes, ethylpentenes, octenes, methylheptenes, dimethylhexenes, ethylhexenes, nonenes, methyloctenes, dimethylheptenes, ethylheptenes, trimethylhexenes, cyclopentene, cyclohexene, methylcyclopentene, cycloheptene, methylcyclohexene, dimethylcyclopentenes, ethylcyclopentenes, cyclooctenes, methylcycloheptenes, dimethylcyclohexenes, ethylcyclohexenes, trimethylcyclohexenes, methylcyclooctenes, dimethylcyclooctenes, ethylcylcooctenes, benzene, toluene, ethylbenzene, styrene, xylenes, methane, ethane, propane, butane, methylpropane, methylbutane, dimethylbutane, pentanes, hexanes, and the like, and combinations of two or more than two of these hydrocarbons.
Furthermore, the fluid feed can contain 0.001 to about 5 weight % hydrogen, and up to 5000 parts per million volume (ppmv) of carbon monoxide.
Also, the feed can contain small amounts, generally less than about 0.05 weight %, in particular about 0.1 to about 400 ppm S, as sulfur compounds, such as H2S, carbonyl sulfide, carbon disulfide, mercaptans, organic sulfides such as dimethyl sulfide, thiophene, organic di-, tri- and tetrasulfides, and combinations of two or more thereof, as impurities.
The selective hydrogenation process of this invention is generally carried out by contacting a feed stream comprising at least one highly unsaturated hydrocarbon and molecular hydrogen with the catalyst of this invention which is generally contained in a fixed bed. Generally, about 0.1 to about 100, preferably about 0.7 to about 30, moles of hydrogen are employed for each mole of the highly unsaturated hydrocarbon present in the feed. The temperature necessary for the selective hydrogenation process of this invention depends largely upon the activity of the catalyst composition, the hydrocarbon feed composition, and the desired extent of hydrogenation. Generally, reaction temperatures in the range of from about 10xc2x0 C. to about 300xc2x0 C., preferably about 20xc2x0 C. to about 250xc2x0 C., and most preferably 30xc2x0 C. to 200xc2x0 C. can be used. A suitable reaction pressure generally is in the range of about 15 to about 2,000 pounds per square inch gauge (psig), preferably 50 to about 1,500 psig, and most preferably 100 to 1,000 psig. The gas hourly space velocity (GHSV) of the hydrocarbon feed can vary over a wide range. Typically, the space velocity of the feed will be in the range of about 500 to about 40,000 liters of hydrocarbon feed per liter of catalyst hour, more preferably about 1,000 to about 30,000 liters/liter catalyst hour. The hydrogenation process conditions should be such as to avoid significant hydrogenation of monoolefins, which are formed by hydrogenation of the highly unsaturated hydrocarbons being initially present in the feed, to saturated hydrocarbons such as alkanes and cycloalkanes.
If it is desired to regenerate the catalyst composition of this invention after prolonged use in a hydrogenation process, this can be accomplished by calcining the catalyst in an oxidizing atmosphere such as in air at a temperature that does not exceed about 700xc2x0 C. to burn off carbonaceous and sulfur deposits. Optionally, the catalyst can be reimpregnating with selectivity enhancer(s) and heated as described above for the production of fresh catalyst composition of this invention.